Space is the biggest Gmail advantage, plus it has pop access so that you can use an external client (Yahoo makes you pay for it). Live also has the pop server for no cost. I use the gmail account for everything, since switching internet providers.
I've been using gmail for some time now, and I like it a lot more than other free e-mail providers such as hotmail and yahoo.
I like gmail because of the storage available but I dislike how they group messages from the same sender together. It makes you miss messages on occasion.